This invention relates to a work vehicle having a swivel platform mounted on a chassis, and work arm assembly mounted for horizontal oscillation on the swivel platform, in which the swivel platform and the work arm assembly are actuated by means of separate hydraulic actuators.
Taking a swivel type backhoe carrying a bucket on a swivel platform as an example of this type of work vehicle, there are two alternative ways of moving the bucket in a horizontal direction between a spot of digging and a spot of depositing removed soil. One is by oscillating the arm assembly horizontally and the other by swivelling the swivel platform. Which method to choose is dependent on the space of the operation site and the like. When digging a ditch alongside a wall or such object by setting the swivel platform and the arm assembly oppositely turned, one of the above two methods is taken and hardly ever are they used simultaneously.
For operating the swivel platform and the arm assembly separately, the known arrangement provides a control valve on a flow passage leading to each of the hydraulic actuators, and two hand levers are selectively operated according to the desired mode of movement.
In short, the swivel platform and the arm assembly are alternatively moved to suit the site and nature of operation, and the hand lever for whichever is selected alone is operated.
The known arrangement as such requires two expensive control valves and has a disadvantage in the matter of safety insomuch that the wrong one of the valves could be operated or they could be switched in the wrong direction.